1. Field of the Invention
The present invention relates to a driving method of a display unit and in particular relates to a charged-particle driving method which can protect a display unit from damaged and increase contrast thereof.
2. Description of the Related Art
The technology focus on a closed space that comprises two electrodes and a spacer, wherein at least one of the two electrodes is transparent. Further, at least one charged-particle with a color dye is distrusted in the closed space. The charged-particle is driven by applying a voltage difference on the two electrodes to generate an electrical field.
Please refer to FIG. 1 which is a schematic of a conventional display unit and a driving method thereof. The conventional display unit has two different driving methods that are respectively shown in the upper part and the bottom part of FIG. 1. For simplification, the driving methods shown in the FIG. 1 are discussed first in the following paragraphs. As shown in FIG. 1, a display unit 1 comprises at least a first electrode 11, a second electrode 13, a first particle 15 and a second particle 17, wherein the first electrode 11 is separated from the second electrode 13 by a distance, and the first particle 15 and the second particle 17 are charged and filled in a space therebetween, and a body of a display apparatus (not shown in FIG. 1). By casting voltage to the first electrode 11 and the second electrode 13 simultaneously or separately, a voltage difference or an electrical field V2 is generated so as to drive the first particle 15 and the second particle 17. In this conventional display unit 1, the first particle 15 moves toward the second electrode 13, and the second particle 17 moves toward the first electrode 11.
Please refer to the upper part of FIG. 1. In order to seek better contrast performance of the display unit 1, the conventional driving method uses the PWM method to drive the display unit 1 and the desired contrast of the display unit 1 can be achieved by adjusting the ON/OFF duration, ratio and the number of pulses. An optimal situation is where the electrical field or a voltage difference V2 generated during the ON duration is large enough to move the particles 15 and 17, and the energy got during the ON duration is large enough to move the particles 15 and 17 until energy exhaustion during the OFF duration, wherein the voltages are turned off during the OFF duration and the particles 15 and 17 are assumed not affected by any other external electric fields. Similarly, the driving method shown in the bottom part of FIG. 1 casts a voltage difference −V1 between the first electrode 11 and the second electrode 13, wherein the voltage difference −V1 is an inverse voltage of the voltage difference V2. The voltage difference −V1 drives the first particle 15 to move from the first electrode 11 to the second electrode 13, and drives the second particle 17 to move from the second electrode 13 to the first electrode 11. The driving method shown in the bottom part of FIG. 1 uses the PWM method to drive the display unit 1 and the desired contrast of the display unit 1 can be achieved by adjusting the ON/OFF duration, ratio and the number of pulses.
There are three ways to vanish the energy: (1) inter-molecular force between particles; (2) hitting other particles or the spacer of the electrode; (3) inter-molecular force between the particle and medium of the closed spaced formed by the two electrodes and the spacer. Due to the unfavorable factors of the characteristic of the particles, the position of the particles, the uniformity of the medium, the attraction force and the repulsion force, the driving method usually uses a single pulse signal with a relative long driving time duration to drive the particles. But to overcome the described unfavorable factors, the driving method uses multiple pulses with relative short driving time duration to drive the particles. Thus, the particles can be stopped at the electrode and are uniformly distributed on the electrode. The longer the ON duration is, the more energy the particle gains. The gained energy causes three phenomenon of the particles: (1) the particle is still moving and the energy gained at the next ON duration accelerates the particle; (2) the particle is motionless and contacts the electrode, and the energy gained at the next ON duration drives the particle to move toward the electrode; and (3) if particles with different polarities are in the same space, the particles with different polarities may attract each other after a previous ON duration, and separate in the next ON duration. The separated particles then move toward a corresponding electrode. During the OFF duration, the electrical field stops applying force to the particles and the particles may continue to move according to the energy gained in the previous ON duration, or the particles move due to the inter-molecular force between particles.
The described three phenomenon have the following disadvantages: (1) The energy gained by the particle during the ON duration is not large enough to overcome the inter-molecular force between particles or between a particle and the electrode; (2) The particle strikes the electrode or other particles with high speed, thus, the particle may be moved or rebounded and this may cause unrecoverable damage to the particles and the electrode; and (3) The particles may be malformed due to the compression caused by the electrical field. The area that the particle touches the electrode may be enlarged and the structure or the characteristic of the particle or the electrode may be changed or affected.
FIGS. 2a, 2b and 2c are schematic diagrams of conventional driving methods. Please refer to FIG. 2a. The conventional driving method shown in FIG. 2a uses a single pulse to drive the particle. This may cause the particle to strike the electrode or other particles at high speed, and the driven particle may continuously squeeze other particles. This may cause unrecoverable damage to the particles and electrode.
Please refer to FIG. 2b. The conventional driving method shown in FIG. 2b uses multiple pulses to drive the particle, wherein a ratio between the ON duration and the OFF duration is fixed, to let the particle move with lower energy, and the particle can be stopped due to the inter-molecular force between the particle and the electrodes during the OFF duration. This driving method requires a longer OFF duration and the total driving time is increased accordingly.
Please refer to FIG. 2c. The conventional driving method shown in FIG. 2c drives the particles to quickly move from one side to another side by adjusting the ON duration, and the total driving time can be reduced. However, this cannot prevent the situation where the particles may directly strike the electrode or other particles at high speed.